What is the difference between the average of first 148 even positive numbers and the average of first 129 odd positive numbers?

Answer: Option A

Average of first 148 positive number
$$\begin{array}{rl}& =\frac{N\left(N+1\right)}{N}\\ & =N+1\\ & =148+1\\ & =149\end{array}$$
Average of first 129 odd number $$=\frac{N^2}{N}=N=129$$
Difference = 149 - 129 = 20